Two forms of ammonia are present in any aqueous environment (e.g., aquarium, pool, hot tub, lake, river, pond, manufacturing container, etc.). Ammonia (NH3), sometimes referred to as ‘toxic ammonia,’ is normally present in lower concentrations than ammonium ion (NH4+), which is considered to be less toxic. ‘Total ammonia’ refers to the sum of ammonia plus ammonium ion levels in a solution.
It is important to know the ammonia concentration in a solution, particularly in an environment where organisms are present, due to its toxicity. Most current visual tests, however, are only capable of measuring ‘total ammonia’ (NH3 plus NH4+). These provide an indirect measure of the ammonia (NH3) concentration, and are therefore at least relevant in estimating, for example, toxic ammonia (NH3) levels in an aqueous system (e.g., aquarium, pool, hot tub, lake, river, pond, manufacturing container, etc.).
The relative levels of the two forms of ammonia (NH3 and NH4+) change, equilibrating between forms, with changes in pH and temperature. The pH effect on the equilibrium between ammonia and ammonium concentration, described by a derivation of the Henderson-Hasselbach equation, is a exponential function:
      [          NH      ⁢      3        ]    =            [              NH        ⁢        4            ]              10              (                  ph          -          pKa                )            Consequently, small changes in the pH result in large changes in the equilibrium balance of the two forms of ammonia. Similarly, temperature effects on the NH3:NH4 equilibrium constant (pKa) which in turn affects interpretation of the Henderson-Hasselbach relationship and prediction of the solution concentration of NH3 Ultimately, the amount of ammonia rises with increases in pH and solution temperature. Sampling variation arising as a result of variation in the temperature, time, and sampling position/location within a given aqueous environment will therefore make interpretation of the Henderson-Hasselbach relationship incorrect. Therefore, in addition to knowing the ammonia content, it is important to know the ammonium (NH4+) and/or total ammonia (NH3 plus NH4+) level to understand potential toxic risk in an aquatic system. In conditions involving high ammonium content and low pH, a rise in pH would result in a subsequent large equilibration shift of NH4+ into a high level of toxic NH3, quickly creating a hazardous situation.
In theory, if the concentration of either the ammonia, or the ammonium, or the total ammonia is determined through testing, in conjunction with the pH of a solution, and the temperature is known, then based on the equilibrium relationship, the concentration of the other parameters can be established. In practice, since both the nitrogenous products in water (e.g., ammonia), temperature and pH levels can constantly vary, and in view of inherent limitations of existing test methods, the measurement and tracking over time of these fluctuating parameters is problematic, particularly with the simple procedures and kits typically used.
Current visual tests for ‘total ammonia’ and pH rely almost exclusively on single-point measurements, typically performed with an extricated discrete sample of the solution to be tested. Additionally, most require addition of reagents that engender non-reversible chemical reactions. Alternatively, there are single-use devices that can be immersed briefly in a solution to be tested, without removing a test aliquot, but contain reagents that are soluble, and that leach, bleed or diffuse from the sensing device. Such devices are only used for instantaneous measurements, at one time point, and are not designed for reversibility or stability with prolonged immersion. Prior art examples of such single-point pH test kits include: a freshwater only pH test kit requiring a sample aliquot of freshwater and using a liquid reagent (Aquarium Pharmaceuticals, Inc.), where the product is only useful for freshwater because its range is too narrow to be applicable to saltwater, which typically has higher pH levels; and a pH dip test using a test strip with an indicator reagent pad (Quick Dip™ pH test; Jungle Laboratories Corporation); and a pH dip test using non-bleeding single-test indicator strips (e.g., COLORPHAST® pH 6.5-10.0; made by EMD Chemicals, Inc. Gibbstown, N.J., USA). Additionally, there is one ‘in-tank’ pH sensor that is a continuous in-tank freshwater only pH sensor (LivepH™ from LiveMeter™ Technologies, Inc.).
Prior art examples of such single point ammonia test kits include: a total ammonia freshwater-only test kit requiring a sample aliquot of freshwater, and using a liquid reagent (Aquarium Pharmaceuticals, Inc.); and a total ammonia test using a test strip with an indicator reagent pad (Ammonia Test Strips, from Mardel). Additionally, one visual test for directly measuring, at least qualitatively, only the toxic ammonia (NH3) has also been developed, which is a continuous in-tank ammonia (NH3) sensor (Ammonia Alert™, from Seachem).
Therefore, on the one hand, a total ammonia value obtained using a ‘total ammonia’ single-point test kit, is somewhat useful in monitoring for potentially toxic conditions. However, depending on parameters such as pH, temperature and spatial positioning where the point measurement is made within an aqueous environment, such total ammonia measurements can be indefinite and/or misleading, with respect to what the actual toxic ammonia level is. On the other hand, prior art determinations of total ammonia, based on independent separate determinations of pH and ammonia, are inherently inaccurate because of thermal, temporal and spatial inhomogeneity; for example, where multiple independent test samples are withdrawn for either pH or ammonia (or for either pH and total ammonia) for testing at differing times from a larger aqueous environment. Additionally, the ‘read-out’ of prior art ammonia measurement devices (the AMMONIA ALERT™ card of SEACHEM™) is qualitative (e.g., safe, dangerous, toxic) and not quantitative, precluding accurate determinations of ammonia (NH3) concentration.
Therefore, prior art methods and devices for measuring ‘total ammonia’ do not provide for accurate determination of ammonia, and independent prior art determinations of pH and ammonia have not afforded accurate quantitative determination of either ammonia or total ammonia (NH3 plus NH4).
Therefore, there is a pronounced need in the art for novel and cost-effective methods and devices for accurately determining pH, ammonia (NH3) and total ammonia (NH3 plus NH4+) in an aqueous environment, and which overcome prior art inaccuracies relating to non-homogeneous sampling, and to spatial, temporal and thermal sampling discontinuities. There is a pronounced need in the art for novel and cost-effective methods and devices for accurate quantitative and continuous determination of pH, ammonia (NH3) and total ammonia (NH3 plus NH4+) in an aqueous environment.
There is, in view of its potential toxicity, also a pronounced need in the art for more sensitive devices and methods to quantitatively measure ammonia to provide for earlier detection of potential problems in both solution (e.g., aqueous) and air environments.